An electronic instrument such as an electronic piano is influenced by, for example, a case at its mount part when music sound is output from a speaker. Accordingly, for each product, a speaker adjusting equalizer (EQ), which is consist of a digital signal processor (DSP) and the like, divides the music sound into a plurality of bands to change frequency characteristics of each music sound. Thus, the speaker adjusting equalizer (EQ) can accentuate and conversely reduce a specific frequency bandwidth (harmonic components, higher harmonics components, or noise components) of each music sound to correct (averaging) and improve (for example, clarification of a sound image) an entire sound quality for outputting natural music sound.
Therefore, as illustrated in FIG. 6, the equalizer consist of the DSP, requires relatively a wide area as a program area in the DSP for realizing this. The natural music sound will be output from the speaker through the speaker adjusting equalizer (EQ), which is realized in the DSP by this program.
On the other hand, a headphone is mostly used when playing the electronic piano and the like at home. In a case of the headphone, unlike the above-described speaker, it is not necessary to consider influence of the mounted part. Accordingly, as illustrated in FIG. 7, the music sound is adjusted to be output to a side of the headphone without pass through a part of the speaker adjusting equalizer (EQ).